The invention relates to pressure-controlled actuating mechanisms for use with tools in wellbores.
Downhole tools for performing various tasks in a wellbore may include valves, packers, perforators, and other devices. A wellbore typically is lined with casing, with a production tubing string extending in the wellbore to produce hydrocarbons to the well surface. Packers may be used to provide a seal between the outer surface of a downhole tool and the inner wall of a casing, liner, or open hole. Perforators, such as perforating guns, are used to create perforations in surrounding formation to enable fluid flow. Valves are used to control fluid flow. To actuate such downhole tools as well as other types of tools, various actuating mechanisms may be utilized, including mechanical, electrical, or pressure-activated mechanisms. Pressure-controlled mechanisms may be activated by pressure transmitted through a tubing, an annulus region between the tubing and the casing, or a separate control line.
A conventional type of pressure-controlled actuating mechanism, such as one used for setting a packer or another type of downhole tool, is activated by differential pressure between the inner bore of the tubing and the annulus between the tubing and the casing. The differential pressure may be raised by increasing the pressure in the annulus region or in the tubing bore. With such actuating mechanisms, however, inadvertent rises or drops in tubing bore pressure or annulus pressure may cause accidental setting of a packer or actuation of another tool, which may cause disruptions in well operation. For example, if a packer is set at the wrong depth, the packer will have to be un-set, which may require the lowering of an intervention tool into the wellbore. If a perforating gun is fired in the wrong place, destruction of downhole equipment may occur.
The inadvertent actuation of a downhole tool may cause a well to be inoperable for some amount of time, which may be costly. In addition, inadvertent actuation of certain types of downhole tools, such as perforators, raises safety concerns. A need thus exists for a pressure-controlled actuating mechanism that is protected from inadvertent activation due to pressure fluctuations.